A simple method to quantify sources of settling particles in lakes: Resuspension versus new sedimentation of material from planktonic production

Abstract

A strong relationship (r > 0.99) between settling particulate inorganic matter (SPIM) and total settling particulate matter (SPM) was observed in 315 samples from sedimentation traps in two Swedish lakes, Lake Erken and Lake Limmaren. This relationship can be used to distinguish between different sources of SPM in pelagic systems when the inflow of allochthonous particulate matter is negligible. It is possible to quantify the proportion of material from planktonic production as well as from sediment resuspension in the flux of settling or suspended particulate matter. Furthermore, fluxes of resuspended organic particles can be quantified and distinguished from fluxes of planktonic organic particles. Although Lake Erken and Lake Limmaren are quite different with respect to trophic level, lake surface area and water depth, the estimated proportion of resuspended particles in sedimentation traps was similar in both lakes. Resuspended particulate matter ranged from 35% of the total settling particulate matter up to 99%, with annual means of 83-94%. Moreover, for both lakes it was estimated that, even in epilimnetic traps, only 2046% (annual means) of the total organic settling particulate matter was from planktonic production, whereas 54-80% (annual means) was from sediment resuspension. This is likely to have important consequences for fluxes of nutrients and contaminants.